Resistors in the power rail? Why?
The example connection was made on a BMW vehicle. This system varies the fan speed by a change in duty cycle of the signal. The fan is at rest at 10% and at maximum speed at 90%. The fan or fans have a constant-voltage supply with the earth return path being switched though the vehicle's electronic control unit (ECM).
now that I moved it to a pref board I cannot control the fans anymore.